1. Field of the Invention
The present invention relates to an antenna module and an electronic device including the antenna module. The antenna module may be included, for example, in a RFID (radio frequency identification) system, a short-distance wireless communication (NFC: near field communications) system, and the like.
2. Description of the Related Art
Antenna coils have been used in short-distance wireless communication such as NFC. Japanese Unexamined Patent Application Publication No. 2014-107573 describes an antenna module that includes a multilayer body of insulator layers and that also includes surface-mounted devices. The antenna module described in Japanese Unexamined Patent Application Publication No. 2014-107573 has a configuration in which via conductors connecting the surface-mounted devices to terminal electrodes are disposed in a center portion located between interlayer connection conductors for an antenna coil which are disposed at the ends of linear conductors, achieving reduction in interference between the antenna coil and the via conductors.
Typically, in many cases, in order that an antenna coil formed in a multilayer body has improved antenna characteristics, the insulator layers are defined by magnetic bodies. To retain the mechanical strength, the outermost insulator layers are defined by nonmagnetic bodies in some cases.
When surface-mounted devices are disposed on the top surface of a multilayer body, mounting electrodes for mounting the surface-mounted devices and insulator layers on which wiring conductors connected to the mounting electrodes are formed need to be further disposed on a surface of the multilayer body for an antenna coil. Therefore, an antenna module having surface-mounted devices becomes larger due to the size of the above-described insulator layers. An attempt to reduce the antenna module in size so as to cancel the increase in size leads to a reduction in the size of the antenna coil, resulting in degradation in antenna characteristics.
In addition, when a high voltage is applied between mounting and terminal electrodes and the wiring conductors, the distance between the mounting and terminal electrodes and the wiring conductors is made larger in order to improve voltage endurance, resulting in an increase in the size of the antenna module. An attempt to reduce the antenna module in size so as to cancel the increase in size makes the size of the antenna coil small, resulting in degradation in antenna characteristics.
A similar problem arises when the outermost layers of the multilayer body are formed of nonmagnetic bodies in order to retain mechanical strength.